1. Field of the Invention
The present invention relates to digital rights management (DRM), and more particularly, to a method and apparatus of playing back content based on DRM between a portable storage and a device, and the portable storage for the same.
2. Description of the Related Art
Recently, DRM has been actively researched and developed. Commercial services using DRM have already been used or will be used. DRM needs to be used because of the following various characteristics of digital content. That is to say, unlike analog data, digital content can be copied without loss and can be easily reused, processed, and distributed, and only a small amount of cost is needed to copy and distribute the digital content. However, a large amount of cost, labor, and time are needed to produce the digital content. Thus, when the digital content is copied and distributed without permission, a producer of the digital content may lose his/her profit, and his/her enthusiasm for creation may be discouraged. As a result, development of digital content business may be hampered.
There have been several efforts to protect digital content. Conventionally, digital content protection has been concentrated on preventing non-permitted access to digital content, permitting only people paid charges to access the digital content. Thus, people who paid charges to the digital content are allowed to unencrypted digital content while people who did not pay charges are not allowed to. In this case, when a person paid charges intentionally distributes the digital content to other people, however, the people can use the digital content without paying charges. To solve this program, DRM was introduced. In DRM, any one is allowed to freely access encoded digital content, but a license referred to as a rights object is needed to decode and execute the digital content. Accordingly, the digital content can be more effectively protected by using DRM.
The concept of DRM is illustrated in FIG. 1. DRM relates to management of contents (hereafter, referred to as encrypted contents) protected using a method such as encryption or scrambling and rights objects allowing access to the encrypted contents.
Referring to FIG. 1, a DRM system includes user devices 110 and 150 wanting to access content protected by DRM, a contents issuer 120 issuing content, a rights issuer 130 issuing a rights object containing a right to access the content, and a certification authority 140 issuing a certificate.
In operation, the user device 110 can obtain desired content from the contents issuer 120 in an encrypted format protected by DRM. The user device 110 can obtain a license to play the encrypted content from a rights object received from the rights issuer 130. Then, the user device 110 can play the encrypted content. Since encrypted contents can be circulated or distributed freely, the user device 110 can freely transmit the encrypted content to the user device 150. The user device 150 needs the rights object to play the encrypted content. The rights object can be obtained from the rights issuer 130. Meanwhile, the certification authority 140 issues a certificate indicating that the contents issuer 120 is authentic and the user devices 110 and 150 are authorized devices. The certificate may be embedded into the user devices 110 and 150 when the devices are manufactured and may be reissued by the certification authority 140 after a predetermined duration has expired.
DRM protects the profits of those producing or providing digital contents and thus may be helpful in advancing the digital content industry. Although a rights object or encrypted content can be transferred between user devices 110 and 150 using mobile devices, as shown in FIG. 1, the transfer is inconvenient as a practical matter. Accordingly, to facilitate move of rights objects and encrypted contents between devices, efficient move of data between a device and a portable storage device intermediating between the devices is desired. In other words, a method enabling a device to access content protected by DRM using a rights object included in a portable storage is desired.